A stroller becomes necessary equipment for a family when the parents need to take their baby out, and it is usually designed in a collapsible form to facilitate transporting/storing. For instance, US patent application publication No. 2003/0201626 A1 has disclosed a collapsible stroller. Modern stroller usually has a number of attachments added thereto, such as, a child tray, a parent console, and grocery bag, etc., so as to improve the comfortableness and/or usage convenience of the stroller. These attachments make the volume of the stroller much bigger, and complicates the structure of the stroller, and causes the stroller is not easy to operate to its collapsed state and the stroller is unable to be fully collapsed. Thus, even the stroller is folded into its collapsed state its volume is still relatively large and is not easy for a user to carry and needs a large space for transporting/storage. In addition, due to its collapsible feature, a collapsible stroller may be put into use carelessness by the user before it locked in its completely expanded and this may cause the baby's limbs being injured by accidentally by getting caught between foldable components of the stroller.
Therefore, there exist a need for a collapsible stroller which not only can allows a user easy to operate the stroller to a collapsed state with a compact size but also can ensure that the stroller is used in a fully locking expanded state to avoid accident.